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Message-ID: <469E2A68.6010307@gmail.com>
Date: Wed, 18 Jul 2007 23:57:44 +0900
From: Tejun Heo <htejun@gmail.com>
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To: Satyam Sharma <satyam.sharma@gmail.com>
CC: Gabriel C <nix.or.die@googlemail.com>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Christoph Lameter <clameter@sgi.com>, gregkh@suse.de,
       miles.lane@gmail.com
Subject: Re: [PATCH] sysfs: kill an extra put in sysfs_create_link() failure
 path
References: <a781481a0707142239l397672c6p4fd1dc8dfb73e07c@mail.gmail.com>	 <a781481a0707151414l3efcd2d0q93db88a32b90e344@mail.gmail.com>	 <469A9D5D.10509@googlemail.com> <469B61C8.8010902@googlemail.com>	 <a781481a0707160819w1be9128cxb3cdd06ba068b20d@mail.gmail.com>	 <469BB7B8.3060002@gmail.com> <469BB9CA.6090500@googlemail.com>	 <469BC2D6.5090008@googlemail.com> <469BC34C.4080107@googlemail.com>	 <20070718071445.GI23568@htj.dyndns.org> <a781481a0707180748j4760ab8bo237c1abc02feb593@mail.gmail.com>
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Satyam Sharma wrote:
> On 7/18/07, Tejun Heo <htejun@gmail.com> wrote:
>> There is a subtle bug in sysfs_create_link() failure path.  When
>> symlink creation fails because there's already a node with the same
>> name, the target sysfs_dirent is put twice - once by failure path of
>> sysfs_create_link() and once more when the symlink is released.
> 
> The "symlink" is released? But the creation of the symlink is
> precisely what failed here ... did it not?
> 
>> Fix it by making only the symlink node responsible for putting
>> target_sd.
> 
> And again ... the changelog sounds confusing indeed, perhaps I'm
> not familiar enough with sysfs symlink-related terminology/semantics.
> Care to elaborate?
> 
>>         sd = sysfs_new_dirent(name, S_IFLNK|S_IRWXUGO, SYSFS_KOBJ_LINK);
>>         if (!sd)
>>                 goto out_put;
>> +
>>         sd->s_elem.symlink.target_sd = target_sd;
>> +       target_sd = NULL;       /* reference is now owned by the
>> symlink */
> 
> Wow. This looks like a very mysterious way to fix a mysterious bug :-)
> BTW I just looked over at sysfs_create_link() and ... it looks quite ...
> unnecessarily complicated/obfuscated ...

Well, I dunno.  Probably my taste just sucks.  Please feel free to
submit patches and/or suggest better ideas.

-- 
tejun